Build a non-stripped rust-coreutils binary for dh_setup_copyright

Rust binaries stripped at linking time are smaller than binaries stripped with dh_strip. Since we want the smaller binary possible for rust-coreutils, we strip debug symbols at linking time, but that means dh_setup_copyright is then not able to extract required data. As a workaround we build here a non-stripped binary only for dh_setup_copyright. See infrastructure/apertis-issues#431

This is only a workaround until we can get an equally small binary with dh_strip.